1. Field of the Invention
The present invention relates in general to compressors, and more particularly to compressors of a rotary type which is suitable for use in an automotive air conditioning system. More specifically, the present invention is concerned with rotary compressors of a type in which a measure is employed for adjusting the amount of lubrication oil fed to frictionally engaged members, such as bearings for a rotation shaft and the like.
2. Description of the Prior Art
Hitherto, various rotary compressors have been proposed and put into practical use particularly in the field of automotive air conditioning system.
In order to clarify the task of the present invention, one of the conventional rotary compressors will be described prior to making a detailed description of the present invention.
FIGS. 5 and 6 show the conventional rotary compressor which is disclosed in Japanese Utility Model Second Provisional Publication 61-187991.
As is seen from FIG. 5, the compressor comprises a casing 1 in which a cylinder 2 is stationarily installed. The cylinder 2 is sandwiched between front and rear side blocks 4 and 5. Although not shown, bolts are used for uniting the cylinder 2 and the front and rear side blocks 4 and 5.
As is seen from FIGS. 5 and 6, the cylinder 2 is formed with an oval bore 3 with which a rotor unit 6 is incorporated. The rotor unit 6 comprises a shaft 10 and a rotor proper 7 which is connected to the shaft 10 via spline connection. As is seen from FIG. 6, the rotor proper 7 is rotatably disposed in the oval bore 3 having two crescent clearances defined therebetween. That is, each clearance is defined between an outer surface of the rotor proper 7 and an inner surface 3a of the oval bore 3. The rotor proper 7 is formed with five radially extending vane grooves 9 each receiving therein a sliding vane 8.
When the rotor proper 7 is rotated by a drive means such as engine or the like, the sliding vanes 8 are forced to project outward due to generated centrifugal force, which causes tops of the vanes 8 to contact to and slide along the rounded inner surface 3a of the oval bore 3. As will be described hereinafter, in addition to the centrifugal force, a hydraulic pressure is constantly applied to rear ends of the sliding vanes 8 to bias the same radially outward under operation of the compressor.
Due to rotation of the rotor proper 7, a coolant is introduced into compression chambers C through an inlet port 11 formed in the casing 1 and an inlet opening 12 formed in the front side block 4, as is indicated by arrows illustrated by broken lines in FIG. 5. Each compression chamber C is defined by adjacent sliding vanes 8, the outer surface of the rotor proper 7 and the inner surface 3a of the oval bore 3.
As is seen from FIG. 6, with rotation of the rotor proper 7, each compression chamber C varies the volume and thus the coolant in the compression chamber C is pressurized. As is seen from FIG. 5, the pressurized coolant is then led into a connection passage 15 through a discharge opening 13 of the cylinder 2 against a discharging valve 14. Designated by reference numeral 14a is a protection plate for the valve 14. The pressurized coolant flows in the connection passage 15 and impinges against an oil separator 16 which projects into a space "S" defined in the casing 1. The coolant is then discharged to the outside through an outlet port 17.
When the coolant impinges against the oil separator 16, any oil O is separated from the coolant and falls into an oil reservoir 18 which forms a lower portion of the space "S". As shown, the oil reservoir 18 is defined by a bottom wall of the casing 1 and the rear side block 5. Due to the pressure of the pressurized coolant in the oil reservoir 18 as shown by arrows "P", the oil O is forced to flow into both front and rear oil passages 19 and 20. The front passage 19 includes a passage 19a formed in the cylinder 2 and a passage 19b formed in the front side block 4.
The oil O in the front oil passage 19 is led to a front sliding bearing 22f and to a shaft seal 23 and back pressure chambers 24 for the sliding vanes 8. The oil O in the rear oil passage 20 is led to a rear sliding bearing 22r and to the back pressure chambers 24.
A lower portion of the rear side block 5 is formed with an oil inlet opening 30 through which the oil O in the oil reservoir 18 is led into the front and rear oil passages 19 and 20. Lubrication of the bearings 22f and 22r and the sliding vanes 8 is thus achieved.
As shown in FIG. 5, the oil flow from each oil passage 19 or 20 to the back pressure chambers 24 is made through an annular clearance which is defined between the shaft 10 and the front or rear bearing 22f or 22r. Due to the pressure of the pressurized oil in the back pressure chambers 24 as well as the aforementioned centrifugal force, the sliding vanes 8 are biased radially outward, that is, toward the rounded inner surface 3a of the oval bore 3. Some of conventional rotary compressors use a gear pump for pressurizing the oil O in the oil reservoir 18.
The shaft 10 of the rotor unit 6 is constructed of iron, while the front and rear sliding bearings 22f and 22r are constructed of aluminum. As is known, the sliding bearing 22f or 22r is so constructed as to vary the amount of oil fed to a given portion in accordance with the size of a clearance defined between the bearing 22f or 22r and the shaft 10. Accordingly, the amount of oil fed to the sliding bearing and to the given portion varies in accordance with both:
a) the differential pressure between the oil reservoir 18 and the back pressure chambers 24 for the sliding vanes 8, and PA1 b) the size of the clearance between the bearing 22f or 22r and the shaft 10, the size being varied due to a differential thermal expansion and a wearing difference therebetween. PA1 1) Because the orifice members are separate members thrust into the oil passages, there is the possibility of disconnection of the orifice members from the oil passages. In fact, when the compressor is used in an automotive air conditioning system, vibration of the vehicle tends to increase the possibility. PA1 2) Production of the oil passages is difficult or at least troublesome because of the inclined orientation of them. Furthermore, the work for thrusting the orifice members into such inclined passages is difficult. PA1 3) For achieving a stable settlement of the orifice members in the oil passages, the passages should be machined very precisely.
Thus, when the compressor is forced to operate under a highly loaded condition, the temperature of the bearing 22f or 22r increases and thus the clearance between the bearing and the shaft 10 increases. Thus, in this condition, the oil O which can be reserved in the oil reservoir 18 is reduced, which however induces a possibility of conveying a flash gas to the bearings 22f and 22r through the oil passages 19 and 20. This phenomenon tends to lower the output power of the rotary compressor.
As is understood from the line "A" of the graph of FIG. 4, the amount of oil O fed to the bearings 22f and 22r increases in proportion to the temperature of the bearings 22f and 22r.
As is known, when employed in an automotive air conditioning system, the compressor is subjected to ON/OFF operation for keeping the temperature in a vehicle cabin at a predetermined temperature. However, when the compressor is stopped at the time when the clearance between the bearing 22f or 22r and the shaft 10 has been increased to a certain degree due to increase in temperature of the interior of the compressor, the oil O is forced to flow from the oil reservoir 18 to an intake chamber 11' through the front oil passage 19 and the front bearing 22f. That is, under this condition, the intake chamber 11' is relatively low in pressure. When, thereafter, the compressor is restarted, the oil O in the intake chamber 11' is sucked into the compression chambers C and thus pressurized, so that the force needed for driving the rotor unit 6 is increased temporarily.
When the oil reservoir 18 fails to keep therein a sufficient amount of oil O, the durability of the compressor is lowered. In fact, it tends to occur that the tops of the sliding vanes 8 fail to smoothly contact the rounded inner surface 3a of the oval bore 3, which causes generation of noise and vibration of the compressor.
In order to solve the above-mentioned drawbacks, one measure was proposed which is disclosed in U.S. Pat. No. 4,875,835.
In the measure of this Patent, there are employed orifice members which are thrust into oil passages corresponding to the oil passage 19 and 20 of FIG. 5. The oil passages extend obliquely in front and rear side blocks. Due to provision of such orifices, the oil feeding rate to the bearings is reduced, and thus the oil shortage in the oil reservoir is solved. However, even the measure of the Patent has the following new drawbacks.